The body's circulation is facilitated by the heart, the cardiac pump which ensures that fresh blood is supplied throughout the body delivering nutrients to organs and transporting waste products to the body's filtration systems. The heart, illustrated in section in FIG. 5, is a complex organ operating two pumping systems. One pumping system includes the left ventricle (LV) and left atrium (LA) and services the systemic circulation in which oxygenated blood is supplied to the body's organs. Deoxygenated blood is then returned to the right heart. The other pumping system includes the right ventricle (RV) and right atrium (RA) and services the pulmonary circulation, pumping deoxygenated blood from the heart to the lungs where it is re-oxygenated and then returned to the left heart for re-circulation to the body's organs.
Valves in the heart and throughout the body ensure that blood flows constantly in one direction. These include the mitral valve and the tricuspid valve, which separate the atria and ventricles of the left and right hearts respectively. The circulation is dependent on these valves to ensure that the blood is pumped continuously and efficiently through the heart and delivered to the rest of the body.
The tricuspid valve is a complex structure comprising leaflet tissue, chordae tendinae, papillary muscles and a supporting annulus. The tricuspid valve leaflets are a continuous veil of leaflet tissue that attach to the annulus. Three major leaflets are identified, anterior, septal and posterior. The annulus performs multiple functions including maintenance of valvular shape and dimensions.
In some cases, valves in the circulatory system such as the tricuspid and mitral heart valves are deficient or fail. The causes of partial or total heart valve failure include congenital/structural defects, disease and infection. However, the most common cause of valve failure is dilation of the valve annulus. This occurs as part of the generalised cardiac structural dilatation allied to cardiomyopathy and heart failure. The consequences of heart valve failure can vary depending on the seriousness of the failure, but in most cases the heart's efficiency and the efficiency of the circulatory system is seriously affected and complications often result.
Failure or leakage of the heart valves frequently results in mitral/tricuspid valve regurgitation. In the case of the mitral valve, regurgitation results in back pressure in the lungs, whereas tricuspid valve regurgitation can result in high back pressures in the venous circulation. Clearly, this is undesirable for the health of the heart, as well as for the lungs and other organs of the body. Mitral and tricuspid valve failure can lead to ineffective and/or inefficient cardiac pumping, ventricular and atrial enlargement, pulmonary and/or circulatory hypertension, heart failure and in some cases, death.
Methods exist for repairing and replacing cardiac valves and other valves of the body and treatments for mitral valve regurgitation in particular are available. One form of treatment involves replacement of the entire valve. In other cases, the mitral or tricuspid valve annulus may be repaired by placing a biocompatible annuloplasty ring inside the annulus and suturing the ring to the fibrous tissue of the annulus. In this case, the ring constricts the annulus, enabling the mitral or tricuspid valve leaflets to seal during each pumping cycle and reduce or prevent backflow.
Mitral valve replacement and implantation of the annuloplasty ring both require open heart surgery and are therefore major operations. The patient must be placed under general anaesthetic and undergo cardiopulmonary bypass. Concomitant with the seriousness of such procedures are an increase in morbidity and mortality risk, and a slow and painful period of rehabilitation which follows. Post-operative complications are also common and these include infection, thromboembolism, loss of ventricular function and a need for anticoagulation medication.
The implications of tricuspid valve regurgitation have not been well understood in the past and have only recently become a topic of interest. Because of this, the options available for patients experiencing tricuspid valve regurgitation are limited. The location of the tricuspid valve in the right heart complicates treatment because it is less easily accessible than the mitral valve, and it has a more complex triple-leaved structure.
The mitral valve is accessible via the coronary sinus/great cardiac vein (CS/GCV) which has a close anatomical relationship with the lateral border of the posterior annulus. The small cardiac vein has a similar relationship with the tricuspid annulus. However, unlike the CS/GCV, this vessel is small, variable in size and absent in approximately 50% of cases. Therefore, reasonable vascular access to the tricuspid annulus is limited to a right atrial approach.
In the light of the fact that the available forms of treatment for patients experiencing mitral and tricuspid valve regurgitation are high risk, expensive and prone to complications, it would be desirable to address the deficiencies of these approaches and develop a method of treating certain types of valve failure, particularly tricuspid valve failure, which is less expensive, less invasive, and therefore less likely to result in complications after the procedure.
The discussion of the background to the invention included herein is intended to explain the context of the present invention. It is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge in Australia as at the priority date of any of the claims.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.